In a micro-electro-mechanical system (MEMS), a number of elements requiring electricity such as micro-pumps, microprocessors, micro-sensors, micro-actuators, and others are often integrated with one another. Although voltage and current required to drive these elements of the MEMS are very minute in magnitude compared to those consumed in macro-scaled systems, it is difficult to manufacture a power supply for the MEMS that can provide a proper level of the voltage and the current to those elements, as it must be very small in size.
Conventionally, supply of power for the MEMS has been achieved by using a fuel cell and, in some cases, a form of microwaves is used to supply necessary power to drive MEMS. More recently, a need has been recognized for a self power-generation system that semi-permanently generates electricity by using a temperature difference between the MEMS and its external environment, without necessitating a separate external power source. The self power-generation system triggered a study on “autonomous MEMS” which means a system operable semi-permanently in a condition isolated and independent from an external system.
In a known power generator for use in a macro-scaled system, a high temperature section and a low temperature section are provided. Working fluid travels between the two sections in such a manner that the fluid is heated in the high temperature section to work outside, then cooled by the low temperature section, and is returned to the high temperature section, repeatedly. However, it is difficult to apply this principle to a generator for the MEMS due to limitations in volume, a limitation in the relevant micro-fabrication technology, and influences to other electric circuit or electronic circuit components which have to be incorporated with the generator in the MEMS.
Thermoelectric modules have also been conventionally used for power generation in the MEMS. Power generation using the thermoelectric module adapts the Seebeck-effect wherein two different metals are joined to each other and a temperature difference is applied between them to induce a current.
The thermoelectric module is simple in configuration and even when it operates under a small temperature difference condition it can generate electricity commensurate to that small temperature difference. The thermoelectric module could be used to provide a generator suitable for applications of the MEMS as a reliable energy source with its advantages including operation with reduced noise, as it requires no working fluid or parts performing mechanical movement.
However, this type of generator has low operational efficiency and cannot generate sufficient level of electric power because suitable materials are not yet fully developed. For these reasons, this type of generator is not an appropriate power source for, e.g., a micro-pump for the MEMS.
Therefore, there is a need in the art for a micro-electro-mechanical generator capable of providing appropriate levels of electricity for MEMS.